The invention relates to lasers, and more particularly to methods and apparatus for producing ultrashort pulses from a synchronously pumped dye laser efficiently and without sacrificing power, using a new pumping source.
Pulse compression and its uses in providing a narrow pulsewidth pumping source for a synchronously pumped dye laser are known. The shortened width pumping source causes the dye laser to produce an output beam of shorter pulsewidth.
Synchronous pumping is well known as enabling the generation of short tunable pulses from dye lasers. Ausschnitt, Jain and Heritage [C. P. Ausschnitt, R. K. Jain and J. P. Heritage, IEEE J. Quantum Electron. QE-15, 912 (1979); and C. P. Ausschnitt, and R. K. Jain, Appl. Phys. Lett. 32, 727 (1978)] disclosed the use of a pulsed pumping source which may be an argon or a frequency doubled Nd:YAG laser, to synchronously pump a dye laser. In connection with that system the authors discussed the dependence of the dye laser pulsewidth on the width of the pumping pulse, showing that with shorter pump pulses, shorter dye laser output pulses will result. They also predicted that the output pulsewidth from a synchronously pumped dye laser should depend upon the square root of the pump pulse duration.
More recently, A. M. Johnson and W. M. Simpson have synchronously pumped a Rhodamine 6G dye laser and obtained pulses as short as 210 femtoseconds, with 40 milliwatts of average power [A. M. Johnson and W. M. Simpson, JOSA B 2, 619 (1985)]. Their pump source consisted of a continuous wave (CW) modelocked Nd:YAG laser which was first frequency doubled and then pulse compressed to 460 fsec [A. M. Johnson, R. H. Stolen and W. M. Simpson, Appl. Phys. Lett. 44, 729 (1984)].
More typically, dye lasers have been pumped with a cw modelocked Nd:YAG source which is merely frequency doubled, with or without a cavity dumper on the output of the dye laser.
All of these publications are incorporated by reference in this patent application in accordance with .sctn.608.01(p) of the Manual of Patent Examining Procedure of the United States Patent and Trademark Office.
In copending application Ser. No. 729,376, filed May 1, 1985, there is disclosed a pulse compression apparatus capable of compressing a relatively long width optical pulse to a short width pulse. The copending application Ser. No. 729,376 filed May 1, 1985 is assigned to the same Assignee as the Assignee of this application and is incorporated by reference in this application in accordance with the provisions of Section 608.01(p) of the Manual of Patent Examining Procedure of the United States Patent and Trademark Office. The pulse compressor therein utilized a color generator which included an optical fiber, for broadening the bandwith of the long pulse to include any additional colors required for compression to the short pulse. The pulse compressor device also included a grating aligned with the output of the color generator at a grazing incidence angle effective for producing a compact grating structure, reduced ellipticity of the beam output from the compressor and high efficiency of light transmission through the device. The present invention can utilize this type of pulse compression device as a part of the method and system disclosed herein. The pulse compressor of the referenced application is very efficient, and efficiency in pulse compression is important to attaining the maximum benefit of the present invention.
In the prior art, including that listed above, ultrashort dye laser pulses were obtained at about the order of magnitude of pulsewidth of the present invention, but at much lower efficiency and much lower output power. Pulse compression of a pumping source has been used, but in combination with frequency doubling which was performed first, as noted in connection with Johnson and Simpson. None of the systems disclosed in the prior art was able to achieve an ultrashort pulsewidth output from a dye laser, particularly a subpicosecond pulsewidth, at relatively high average power as does the system of the present invention described below.